This invention relates to proton radiography of human subjects.
Diagnostic radiologists are constantly seeking more useful radiographs and other means for internal visualization that minimize the risk of harm to patients. The detection by X-rays of anomalies such as cancers and other tumors is rendered more difficult by the fact that X-rays produce an image by absorption in material through which they pass. This absorption is proportional to the square of the atomic number of the material in the path of the X-rays. Thus, bones, largely calcium, are easy to distinguish and soft tissue, mostly carbon, hydrogen, and oxygen, is not. In particular, cancerous lesions have very nearly the same atomic composition as normal cells. Visualization of such lesions has therefore been accomplished by injection or ingestion of a material of high atomic number which will concentrate in the lesion to increase its opacity to X-rays. A similar means of visualizing lesions in certain parts of the human body involves the administration of compounds containing radioisotopes that are taken up preferentially by the lesions. Each of these means, administration of dense compounds and administration of radioactive compounds, presents a potential threat to the well-being of the patient that would be better avoided if possible.
It is known that one way to avoid the threats outlined above is to expose the suspected lesion to a flux of ions. It is possible to detect differences in the energy loss in a beam of ions when the beam is passed through a substance. This energy loss is proportional to density, and in particular electron density. If a lesions exhibits a difference in density from the surrounding material, this density difference may be detected to provide a picture of the lesion which would be difficult or impossible to attain using X-rays. Other advantages exist from the use of ion beams, particularly beams of protons. Since no tracer or radiopaque material need be administered, there is no problem of delay in obtaining pictures resulting from the time necessary to ingest and distribute such tracer or radiopaque material. In addition, it has proved possible to obtain proton radiographs using extremely low levels of radiation.
The conclusions stated above have resulted from investigative work that has been carried out at various Accelerator Laboratories. Each such study has involved using an accelerator designed for research in high-energy physics in a manner for which the accelerator is marginally adapted. Relative to the needs of diagnostic proton radiography, the particle-research accelerators are expensive to build and complicated and expensive to operate. They produce too many protons in a beam whose particle density across a cross section is too high. The beam they produce is not designed either to be swept or to be defocused into a uniformly diffuse beam. Finally, and this is a serious disadvantage, they are not located in or conveniently near hospitals. The combination of factors outlined above suggests a need for a proton diagnostic accelerator that is sufficiently inexpensive to build and simple to operate and that is sufficiently safe that it can be located and routinely operated in a hospital.
It is an object of the present invention to provide facilities for proton radiography for location in a hospital.
It is a further object of the present invention to provide means located in a hospital for obtaining diagnostic proton radiographs.
Other objects will become apparent in the course of a detailed description of the invention.